I think I remeber hearing that in the OC that taking focus/specialization feats in a weapon increases the chances of getting that weapon in random loot. Does that work in SoU too? I took both weapon focus and weapon specialization in kukri but the best I found so far is a plain kukri +1. I'm just finishing the interlude. Can I expect to find any magical kukris (random or not, even sold from merchants will do) in the next chapter?

Most likely. Assuming ILR is on, you won't find a lot of things beyond what you can actually use, especially in stores. Most of the weapons are in game, it's just a matter of locating where.